1. Field of the Invention
The present invention relates to a zoom lens.
2. Description of the Related Art
In recent years, imaging apparatuses such as digital cameras (digital still cameras) and monitoring-use video cameras equipped with an imaging element, such as a charge-coupled device (CCD) and a complimentary metal-oxide semiconductor (CMOS), have come to be commonly known. Demands placed on these imaging apparatuses, in general, include high image quality and high resolution in a compact and light-weight package. Relatively low manufacturing cost is also desirable. Thus, imaging zoom lenses equipped on such imaging apparatuses are also demanded to be more compact and light-weight with a lower cost.
Consequently, to address such demands, numerous zoom lenses equipped with, sequentially from an object side, a negative first lens group and a positive second lens group, and capable of varying focal length by changing the interval between the first and the second lens groups have been proposed, such as those disclosed in Japanese Patent Application Laid-Open Publication Nos. 2006-39094, 2003-287677, and 2005-250171. Such two-lens-group zoom lenses are advantageous in that a relatively simple lens barrel structure can be configured easily.
The zoom lenses disclosed in the Japanese Patent Application Laid-Open Publications cited above, however, have many shortcomings, particularly as lenses to be equipped on imaging apparatuses of which compactness and high resolution are demanded.
For example, the zoom lenses recited in Japanese Patent Application Laid-Open Publication Nos. 2006-39094 and 2003-287677 are configured by 7 lens elements (3 lens elements in the first group, 4 lens elements in the second group) and thus, the structure is not simple nor is a sufficiently compact size achieved. Furthermore, a glass aspherical lens is employed arising in a further problem of high manufacturing cost.
The zoom lens recited in Japanese Patent Application Laid-Open Publication No. 2005-250171 makes copious use of aspherical lenses to facilitate compactness and high resolution, however, the F number at the wide angle edge is 3.5, dark, arising in a problem with the brightness of the lens.